Over the years the agricultural and forestry industries have turned increasingly to science to help feed and house the ever increasing human population. Through the development of various herbicides, fertilizers, insecticides and pesticides for terrestial crop and forestry uses, man has been able to markedly improve the productivity of the land. The increases in crop and timber production, however, have not been obtained without suffering some adverse consequences.
More particularly, many of the herbicides, fertilizers, insecticides and pesticides that have been developed detrimentally impact the environment in one way or another when used in certain concentrations or under certain conditions. Livestock poisonings, fish kills, and other cataclysmic events have resulted. For example, many insecticides such as DDT are particularly stable and resistant to destruction by light and oxidation. With continued use, concentrations of such insecticides may build up in the environment over time to dangerous levels. This may lead to widespread death of wildlife and contamination of water supplies deleteriously affecting downstream population centers.
The problem has not gone unnoticed by the government. The Environmental Protection Agency has recently devised new tests specifically designed to collect the data necessary for evaluating the hazard inherent in these types of chemicals. One of the studies developed by the government for evaluating the overall environmental impact of, for example, a pesticide, is a full degradation study in water.
When pesticides are introduced into aqueous systems in the environment either directly or by leaching of runoff after terrestrial application, they may undergo photolytic transformation by sunlight. Photolysis is the interaction of a compound with light. More specifically, light energy is transferred to the chemical bonds of the compound, either directly or indirectly through another compound. This energy serves to break the bonds and the original compound is transformed to other compounds known as photoproducts. The purpose of the photodegradation or solution photolysis studies is to obtain data on rates of photolysis and half-lives of the parent pesticide and its photodegradates to establish the importance of this transformation process and the persistence characteristics of photoproducts that may be formed.
Exacting test procedures have been developed to accurately determine the rates of agueous photolysis of pesticides (t.sub.1/2) and to identify photolytic products and rates of formation and decline of these products. The procedures are standardized so that results of various studies, even when conducted by different groups, may be effectively compared.
Preferably, the test samples are exposed to natural sunlight conditions. Thus, the vessels for containing the test samples must be supported in a way so as not to block the passage of light to the samples. In addition, the vessels themselves must be optically pure so as not to filter out any of the radiation of natural sunlight.
A further concern relates to the need to minimize the loss of the test sample through volatilization. In order to accurately determine the photolysis rate of the test sample, the volatiles emitted by the test sample should be collected. Further, these volatile photoproducts should be identified if emitted in any appreciable level. Thus, in order to carry this procedure out, the test sample vessel must be sealed and provide some means for collecting the emitted volatiles. In addition, the test sample solution needs to be available for periodic testing at specific time intervals in order to allow determination of the photoproducts produced within the solution by photolysis.
Past apparatus that have been developed for this purpose have been cumbersome and difficult to use effectively. Such apparatus have actually promoted mistakes during testing that prevent them from providing accurate analytical data in accodance with the rigid test requirements set by the Environmental Protection Agency. A need is therefore identified for an apparatus specially designed for use in performing solution photolysis studies that is simple to use effectively.